One of my colleagues was baffled by why Outlook displayed this message:
You pressed CTRL + ENTER.
Do you want to use CTRL + ENTER as a keyboard shortcut for sending a message?
☐ Do not show this message again.
"I never understood the need for that dialog since I thought Ctrl+Enter meant, by convention, send this message. Then one day a former coworker expressed frustration at the dialog because Ctrl+Enter means soft return. He's a few years older so perhaps its a generational thing? I do notice that the various web based email services differ in how they interpret Ctrl+Enter."
Back in the old days, Ctrl+Enter meant "I'm hitting Enter, but I just want you to insert the Enter character, not execute anything."
From an MS-DOS prompt, Ctrl+Enter inserted a line break but did not execute the command.
In a multi-line edit control on a dialog box, Ctrl+Enter inserts a carriage return into the edit control rather than executing the default button on the dialog box.
But since nobody uses MS-DOS or dialog boxes any more, these historical meanings are gradually being lost, and Ctrl+Enter is pretty much a wide open hotkey that anybody can assign whatever meaning to it they like. (For extra confusion: Some programs use Shift+Enter to insert a carriage return into a field.)
Someday, people won't even remember what Ctrl+Insert and Shift+Insert do. (I still use the first one when working in WinDbg, since the modern hotkey doesn't work; it means "break into the debugger.")